This invention relates to methods and apparatus for cutting wood, particularly to the use of a resaw for cutting elongate wood cants.
In the lumber products industry it is frequently necessary or at least desirable to utilize a resaw apparatus in a sawmill or lumber yard for cutting wood cants, that is, wood members which have been cut from a log but are destined for further cutting. A resaw is a type of saw utilized to break down cants into smaller pieces, ordinarily to edge a cant or to rip it to the proper thickness. Such a resaw is used, for example, in a sawmill to reduce relatively thick cants coming from a headrig in order to enable more logs to go through the headrig in a given time period, or in a planing mill to reduce the size of boards after they have been planed. In general a resaw is utilized to cut cants to a useful size for whatever purpose they are needed.
Resaws typically incorporate bandsaws and some type of mechanism for feeding the cant to the bandsaw blade. Bandsaws are ordinarily used in such resaw apparatus because they can be constructed with a relatively thin kerf, which minimizes the wood cut from the cant and, therefore, the amount of wood wastage. The feed mechanism typically utilizes a fence or some other means for controlling the direction of the cant as it is urged against the saw blade, and one or more powered rollers for urging the wood cant along a predetermined path into the blade. Where more than one roller is used, the rollers are ordinarily synchronized through the use of elongate axial shafts and gear mechanisms connecting the rollers with one another and with a motor. Although circular saws are sometimes utilized in resaws, they have heretofore only been utilized where the amount of wood removed by a relatively thick-kerfed circular saw blade is acceptable.
There are several problems with conventional resaw apparatus which limit their speed and accuracy, and result in frequent and sometimes extensive maintenance, thereby limiting the productivity of such apparatus. One problem is that, by their nature, bandsaws are relatively slow cutting saws. In addition, bandsaw blades tend to wear relatively faster than, for example, circular saw blades, and when a blade becomes dull it tends to be pushed off its drive wheels by the wood that it is cutting if an attempt is made to maintain the speed of the wood past the blade. Moreover, the accuracy of such a resaw is reduced by such an attempt to maintain speed with a dull saw blade.
It has been recognized, for example in E. Williston, Lumber Manufacturing: The Design and Operation of Sawmills and Planer Mills 134-39 (1976), Library of Congress Catalog Card No. 76-6718, that the use of circular saws in resaw apparatus would be desirable because of their relatively low cost, low profile, easy maintenance and simple, rugged construction. Moreover, circular saws provide high speed, less expensive blade sharpening and longer wear than bandsaws, and more resistance to the pressure produced by attempting to maintain cutting speed when the blade is dull. However, circular saws ordinarily require a relatively thick kerf, since a thin-kerfed blade tends to waver in position due to the pressure from the wood that it is cutting and the heat generated by cutting, thereby producing an incaccurate cut.
In addition, the known means for feeding a cant to the cutting blade of a resaw are typically not easily adjustable for direction, centering or cant thickness. Moreover, the complex mechanisms which urge a cant against the cutting blade, often utilizing rollers mounted on elongate axles and connected by gear linkages, reduce in accuracy with wear and must usually be rebuilt in order to eliminate this inaccuracy. Accordingly, there is a need for an improved resaw apparatus and method for increasing the speed of cutting cants while maintaining or improving accuracy and minimizing maintenance.